The present invention relates to a pharmaceutical composition being useful as a secondary cataract inhibitor.
More particularly, the present invention relates to an inhibitor for secondary cataract after cataract surgery, which inhibitor comprises as the active ingredient N-(3,4-dimethoxycinnamoyl)-anthranilic acid represented by the formula: 
or a pharmaceutically acceptable salt thereof.
Cataract is a refractory ocular disease which occurs and develops due to various factors. The discase subsequently leads to lower vision due to lens opacity. Most of this ocular discase is age-related senile cataract. The incidence of cataract is thought to be 60-70% in persons in their sixties and nearly 100% in persons eighty years old and more. In proceeding toward a society composed largely of elderly people, the prevention and treatment of cataract will become more important for the future. However, at the present time, there is no sure therapeutic agent which has an inhibitory activity on the development of cataract. Therefore, the development of an effective therapeutic agent has been desired. Presently, the treatment of cataract depends upon the correction of vision using eye glasses, contact lenses etc. or surgical operations such as insertion of an intraocular lens into the capsula lentis after extracapsular cataract extraction.
In cataract surgery, the incidence secondary cataract after surgery is been a problem. Secondary cataract is equated with opacity present on the surface of the remaining posterior capsule following extracapsular cataract extraction. The mechanism of secondary cataract is mainly as follows. After excising lens epithelial cells (anterior capsule), secondary cataract results from migration and proliferation of residual lens epithelial cells, which are not completely removed at the time of extraction of the lens cortex, onto the posterior capsule leading to posterior capsule opacification. Also, secondary cataract results from abnormal proliferation of the residual lens epithelial cells in the equator followed by formation of Elschnig pearls.
In cataract surgery, it is impossible to remove lens epithelial cells completely, and consequently it is difficult to always prevent secondary cataract. It is said that the incidence of the above posterior capsule opacification is 40-50% in aphakic eyes and 7-20% in pseudophakic eyes.
On the other hand, in the field of cataract medication, extensive study has been actively promoted in order to find substances capable of inhibiting secondary cataract. Up to now for example, it has been was confirmed that metabolic antagonists such as mitomycin, daunomysin, 5-FU and colchicine are effective secondary cataract inhibitors. However, concerns about these drugs have been raised in view of problems such as serious side effects which have been found [Atarashii Ganka, Vol. 12, No. 3, pp 451-452 (1995); Japanese Journal of Ophthalmic Surgery, Vol. 8, No. 3, pp. 439-446 (1995)] and accordingly, these drugs have not been used to use clinically. It has also been reported that the formation of secondary cataract was significantly inhibited when an inserted intraocular lens was coated with indometacin. Further ethylenediaminetetraacetic acid (EDTA) has been found effective in inhibiting secondary cataract [Japanese Journal of Ophthalmic Surgery, Vol. 8, No. 3, pp. 439-446 (1995); IOL and RS, Vol. 19, No. 2, pp. 78-82 (1995); Japanese Patent Application Publication (kokai) No.Hei. 8-175984]. However, clinically satisfactory drugs for preventing and inhibiting secondary cataract have not yet been developed.
N-(3,4-dimethoxycinnamoyl)anthranilic acid (generic name: Tranilast) represented by the above formula (I) of the present invention has been widely used in medicines for the treatment of allergic disorders such as bronchial asthma, allergic rhinitis, atopic dermatitis and allergic conjunctivitis, as well as cutaneous disorders such as keloid and hypertrophic scar. For example, it has been known that Tranilast has inhibitory activities on chemical mediator release caused by an allergic reaction, excessive collagen accumulation by fibroblast cells in cutaneous tissues and excessive proliferation of smooth muscle cells in coronary artery vessels.
However, it has not been previously disclosed that Tranilast has an inhibitory activity on secondary cataract formation and it until now has not been known that Tranilast is can be useful as an inhibitor for secondary cataract.
The present invention relates to a secondary cataract inhibitor which comprises as the active ingredient N-(3,4-dimethoxycinnamoyl)anthranilic acid represented by the formula: 
or a pharmaceutically acceptable salt thereof.
The present invention also relates to a method for the prevention or treatment of secondary cataract which comprises administering N-(3,4-dimethoxycinnamoyl)anthranilic acid represented by the above formula (I) or a pharmaceutically acceptable salt thereof.
The present invention also relates to use of N-(3,4-dimethoxycinnamoyl)anthranilic acid represented by the above formula (I) or a pharmaceutically acceptable salt thereof for the manufacture of a pharmaceutical composition for the prevention or treatment of secondary cataract.
Furthermore, the present invention relates to use of N-(3,4-dimethoxycinnamoyl)anthranilic acid represented by the above formula (I) or a pharmaceutically acceptable salt thereof as a secondary cataract inhibitor.